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Power Over Ethernet

Power over Ethernet (POE) allows you to very simply install network cameras (or other network devices such as VOIP phones) with just a single network cable.

We get a lot of queries about POE, so we’ll try to give you a quickand simple explanation:

An ethernet network is the standard format of network cabling that you use to connect your networked and other devices.

The cables used are commonly known as Cat5 cable (other variants such as Cat5e and Cat6 are available).

The plugs on the ends of the network cables are terminated in RJ45 connectors.

Each Cat5 network cable contains four pairs of cable cores, all of these cores are terminated in the RJ45 plugs, but only two of the pairs are actually used for the transmit and receive signals used by the network for data transmission.

This means that there are two pairs of spare cable cores available within every network cable.

Quite simply these can be used to carry power, electricity, volts & amps to devices on the network.

There’s an IEEE standard governing the proper format and use of Power over ethernet, and the basic version of this is the 802.3af standard. This standard governs things such as the configuration and use of the spare cores and the voltage used being common in all 802.3af compliant devices (nominally 48 volts DC). This relatively high voltage is used to enable the power feed to be useful over relatively long distances – up to 100m. If a lower voltage was used, the voltage drop caused by the cable length might render the even lower voltage arriving at the far end useless for powering the camera.

So, you can take a device known as a poe power injector and place this at the source end (PC, control room …) and route your network cable through the power injector on its route to the camera.

At the camera end, if the camera is a POE enabled device (has 802.3af compliant POE built-in) you can plug the far end of the network cable directly into the rear of the camera and the internal camera circuitry will split-out from the network cable the power that it needs to operate. In this way just a single network cable is all that is required to both feed power to the camera and to take the IP video signal away from the camera and back to the PC or other recording device.

This Power Over ethernet solution makes for really simple low-voltage installations without the need for a specialist electrical installation contractor, or the requirement for mains or other power cables. Hence, you save not only labour costs but also the cost of a second copper cable.

If the camera or network device does not have built-in POE compatibility, it is still possible to use Power over Ethernet by deploying a device called an Active Splitter at the camera end of the network cabel. An active splitter (as the name implies) is simly an electronic gadget which splits the power and data signals from the one combined network cable to the two cables that a non-POE device requires; one cat5 for data, one power for the camera supply. NB if you are using a splitter be sure to select a device which is able to transform from the 48V carrier signal used in POE down to the correct voltage for the camera you are using (likely to be 3.3V, 5V, 9V, 12V or similar) and is able to present the power in the correct physical format to plug into the rear of the camera e.g. 4.5mm barrel connector.

So, as you can see from the above, the basics of power over ethernet are simple, but there are a few potential pitfalls to catch out the unwary. If you need any help with selecting the correct POE devices for your application please just give us a call.

use-IP Ltd supply a range of POE devices.

Further explanation of Power Over Ethernet

Wikipedia

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